The invention is relates to CVI/CVD furnace apparatus. More specifically, the invention is directed to a sealed gas inlet for a high temperature CVI/CVD furnace.
Processing of refractory composites takes place at elevated temperatures. Such processing includes CVI/CVD deposition of a binding matrix within a fibrous preform structure, and heat treating refractory composites. The reactant gas inlet that introduces the reactant gas into the furnace volume passes through the susceptor floor in the furnace. In prior art furnaces, the gas inlet is not sealed to the susceptor floor and reactive gasses may leak from the volume enclosed by the susceptor and pass over and around furnace components outside the susceptor. Reactive gasses include the reactant gas used in the CVI/CVD process and gasses that are generated during heat treatment processes of refractory articles, for example carbonization of oxidized polyacrylonitrile fiber preforms. The reactive gas may attack furnace components. Porous insulation disposed around the susceptor is particularly susceptible to attack and degradation. The inlet is not sealed in order to allow it to move relative to the susceptor floor during heating and cooling of the furnace. Therefore, a gas inlet is desired that inhibits reactive gas from passing through the susceptor floor while allowing the gas inlet to move relative to the susceptor floor due to differences in thermal expansion and contraction.